canSendMessage

Determines whether the user can send a message in the current state.

This function checks both channel-level capabilities and user preferences to determine if a message can be sent. The required capability depends on the current message mode:

• In thread mode: requires ChannelCapabilities.SEND_REPLY capability

• In regular mode: requires ChannelCapabilities.SEND_MESSAGE capability

The final decision also considers the MessageComposerState.sendEnabled flag, which allows temporary disabling of sending (e.g., while uploading attachments or validating input).